sendPhoto using TelegramBot (exporting to multy-part form data format)

I created a telegram-bot and I execute requests to the telegram bot API from Mathematica. You can find full API documentation here.
I have a problem with sending image from computer or RAM. I try send photo using this code:

I did not manage to solve the problem. But I looked at the full text of the query, which is generated by libraries in other languages. I managed almost exactly to repeat everything, but still I can not send the image.

Thank you, yes, I tried to do so and, strange as it may seem, it worked.
But this works only for a file on disk. Solution - create a temporary file, but how to send it from RAM, I still do not understand.

The length in bytes is right. If you delete this header (content-length) then the result will not unchanged. At the moment there is no difference with the use of base64 and without it. Both of ways returns status code 400 and the message "Bad Request: there is no photo in the request"